The need frequently arises for high intensity pulsed light sources. Pulsed light sources are typically used for signaling applications such as marine navigation, airport signaling and vehicle signaling. Such pulsed light sources are required in different colors and are required to operate over a range of duty cycles and pulse widths. In addition, the pulsed light source must have high intensity and a long operating life.
Light sources designed for continuous use often do not operate satisfactorily in a pulsed mode, since continuous light sources usually require a warmup period and operate most efficiently at elevated temperatures. When a light source designed for continuous use is operated in a pulsed mode, the desired operating temperature is never reached.
The lamps most commonly used for pulsed applications are high pressure, rare gas lamps such as xenon flashlamps. The pressure within the lamp tube may be 20 atmospheres or more at room temperature. Xenon flashlamps have a number of disadvantages. Since they are high pressure lamps, there is a risk of explosion. Such lamps must be carefully handled and must be operated in an enclosure. In addition, xenon flashlamps produce very short light pulses, on the order of microseconds, due to a self-extinguishing characteristic. The duration of the light pulse cannot be lengthened appreciably. The short light pulses are a problem in applications, such as navigation, where the human eye is required to locate the light source. The human eye perceives the short light pulse, but is unable to localize it.
A further drawback of high pressure xenon and other high pressure rare gas lamps is sputtering of electrodes which limits operating life. The sputtering occurs due to bombardment of the cathode by energetic ions within the lamp envelope.
Tungsten filament lamps can be utilized in pulsed applications. However, tungsten filament lamps do not provide the desired efficiency and have a limited life, particularly in applications subject to mechanical shock, such as aircraft and shipboard applications.
It is well-known to use mercury as a fill material in discharge lamps. Upon excitation, mercury produces ultraviolet radiation. A number of prior patents have disclosed discharge devices utilizing a pool of mercury sealed within the discharge envelope. These patents include U.S. Pat. Nos. 1,225,332 (Hewitt); 1,451,271 (Rentschler); 1,554,720 (Ferguson); 1,267,199 (Ferguson); 1,943,847 (Spaeth); 2,841,731 (DeLany et al); 1,903,494 (Beck); and 1,903,495 (Beck). It is believed that all of the disclosed devices were intended for continuous use or were intended for applications other than lighting.
It is a general object of the present invention to provide improved pulsed light sources.
It is another object of the present invention to provide a pulsed light source having a long operating life.
It is a further object of the present invention to provide a pulsed light source that can be operated over a range of light pulse widths and duty cycles.
It is yet another object of the present invention to provide a pulsed light source that can easily be provided in different colors.
It is still another object of the present invention to provide a low pressure, pulsed light source.
It is a further object of the present invention to provide a pulsed light source that is operated at or near ambient temperature.
It is a further object of the present invention to provide a pulsed light source having a combination of the above features.
It is yet another object of the present invention to provide a pulsed ultraviolet radiation source.